The Origin of Earth’s Water

Credit: Kellie Holoski/Science.

Earth is an ocean world with approximately 70 percent of its surface covered with water. In addition, a quantity of water equal to several Earth-size oceans is thought to be contained in the deep interior of the planet. However, the origin of this water remains a puzzle. A special group of meteorites called enstatite chondrites shows a close resemblance to the isotopic composition of Earth and so are hypothesized to represent the major building blocks of Earth. Traditionally, however, enstatite chondrites have been considered to be too dry to contribute significantly to Earth’s water budget. Therefore, Earth’s water was thought to have been delivered later by volatile-rich comets and asteroids, originally formed in the outer solar system, impacting Earth. But what if the hydrogen content of enstatite chondrites, and thus their water-forming potential, has been underestimated?

A recent study led by Laurette Piani from the Centre de Recherches Pétrographiques et Géochimiques (Université de Lorraine, France) and colleagues analyzed 13 pristine enstatite chondrites to determine their hydrogen abundances and isotopic compositions. They found that although enstatite chondrites contain less hydrogen than ordinary and carbonaceous chondrites, more volatile-rich meteoritic materials formed elsewhere in the solar system, they nevertheless contain enough to account for Earth’s water budget. Additionally, the hydrogen and nitrogen isotopic compositions of these meteorites are similar to those of terrestrial rocks, suggesting that the enstatite meteorites could be the major sources of water on Earth. These results support the simple explanation that Earth accreted from hydrogen-rich materials rather than more complicated scenarios that require migration of the giant planets to scatter sufficient bodies into the inner solar system to deliver volatiles to Earth after its formation. READ MORE